The Effect of Bi Concentration on Wettability of Cu Substrate by Sn-Bi Solders

In the present work, the wettability and interfacial tension between Cu-substrate and Sn–Bi solder were examined. The variables of this experiment used the content of Bi, types of flux and soldering temperature. Through analyzing the experimental result concerning wettability, it was found that the role of Bi was diminishing wettability of Cu substrate during soldering. The increasing Bi contents made liquid solder-Cu substrate interfacial tension (γsl) go up. Consequently, the increasing liquid solder-Cu substrate interfacial tension (γsl) led to the degradation of wettability in solder. The rates of wetting can be controlled by the interfacial energy between liquid solder and substrate. This paper describes the effect of Bi element on the wettability of Sn–Bi solders.